Metastasis of prostate cancer is the primary cause for the mortality of patients. Prostate cancer (PCa) that initially develops in the prostate gland is curable by surgery and radiotherapy. However when the cancer has spread to other parts of the body, the choice of treatment is by androgen ablation since PCa cells survive on the availability of androgen hormone. Although this treatment approach is effective initially, PCa recur invariably and do not respond to hormonal therapy. Furthermore, patients undergoing hormonal therapy also develop frequent bone complications and bone loss. Hence, there is an urgent need to develop effective and safe treatment alternatives such as compounds derived from diet to successfully control this cancer and the associated pathology. Vitamin k2 (VK2), a natural menaquinone present in spinach, cheese and meat products has several medicinal values including anti-osteoporosis effect and anti-cancer activity. Experimental and clinical studies suggest that VK2 to be a safe vitamin. Importantly, recent epidemiological studies point inverse relationship of low dietary intake of VK2 and fatal PCa. Our recent published study showed that VK2 inhibits both androgen-dependent and androgen-independent prostate tumor growth in nude mice model. However, the therapeutic benefits of VK2 has not yet evaluated against PCa metastasis. Our preliminary results have shown that VK2 inhibits the expression of Akt, High Mobility Group Box 1(HMGB1) and NF-kB while activating the expression of a putative metastasis suppressor gene namely nuclear receptor subfamily 2, group F, member 1 (NR2F1) in PC-3 bone metastatic PCa cells. Based on our preliminary data, we hypothesize that VK2 induces anti-PCa metastatic effect by inhibiting Akt-HMGB1- NF-kB axis and activating NR2F1 expression in PCa cells. The overall objective of this application is to explore the anti-metastati potential and mechanisms of VK2 using in vivo and in vitro models of PCa. This application has two aims. In Aim 1, we will test whether VK2 inhibits prostate tumor metastasis to the lung and liver following intravenous injection and bone metastasis following intratibial injection, and whether these events are associated with NR2F1 upregulation and inhibition of osteoclastogenesis in bone metastases. In this study, we will also determine whether silencing the intervention marker, NR2F1 will abrogate the effects of VK2 on PCa metastasis. Histopathology will be performed to study the effects of VK2 on the prevention of metastasis nodules in lungs and liver. Expression of Akt, HMGB1, NF-kB (p65), NR2F1, MMP2 and MMP9 in the samples will also be determined by immunohistochemistry. Bone tumor sections obtained from the intratibial model of PCa will also be subjected to histopathology, and immunohistochemistry to study the effects of VK2 on the expression of Akt, HMGB1, NF-kB (p65), NR2F1, RANKL, osteopontin, carboxylated osteocalcin (cOC), bone matrix Gla protein (MGP). Osteoclast formation in the bone samples will be detected by staining for Tartarate Resistant Acid Phosphatase (TRAP) activity. In Aim 2, we will delineate how VK2 mediates its anti-metastatic effects and prevents osteoclastogenesis formation using in vitro studies. In this study, we will be employing variety of approaches such as gene silencing, pharmacological intervention, ChIP, motility, invasion, Western blot, and TRAP assays. Results obtained upon successful completion of these proposed specific aims will yield valuable information in developing VK2 as a potential therapeutic agent in managing PCa metastasis that will ultimately help prolong the life span of the patients.